论青藏高原隆起作用于大气的临界高度

在以前工作〔１０〕的基础上，从大气动力学、热力学及气候学的角度，进一步论证了在青藏高原隆起过程中存在一个临界高度ｈｃ〗（～１．５—２ｋｍ）。当高原隆起突破这一临界高度时才开始对大气产生强烈的作用，从而造成大气环流、大气热力结构、亚洲区域以及全球气候等一系列巨大转变。

A review of POPs in the fragile critical zone of the Tibetan Plateau: transport and transformation

The near-surface environment of the Tibetan Plateau is a fragile critical zone. Our understanding of the transport and transformation of persistent organic pollutants(POPs) in the ecosystem has significantly improved with research conducted in recent decades. In the current study,POP concentrations in soils logarithmically decreased and fractionated with increasing distance from the source area,patterns attributed to air–soil exchange. Transport from soils resulted in the enrichment of POP concentrations in plants and sediments. The enantiomeric fraction indicated that transformation of POPs in soils was significantly correlated with altitude. At the same time, the chiral signature of POPs in soils was maintained from soils to sediments, while the chiral transformation from soils to plants was found to be complex.

Sequestration of carbon as carbonate in the critical zone：insights from the Himalayas and Tibetan Plateau

The carbon pool stored in soil carbonate is comparable to the soil organic carbon.Therefore,secondary calcite precipitation in supersaturated catchment could be an important,yet poorly constrained,carbon sink within the modern global carbon cycle.The chemical analysis of some dissolved species transported by rivers,such as elevated Sr/Ca and Mg/Ca ratios but also heavy stable Ca isotopic compositions,witness the formation of secondary calcite in rivers draining arid regions.However,in areas affected by active tectonics and rapid physical erosion,co-variations in the fluvial Sr/Ca and Mg/Ca ratios could also be related to incongruent carbonate weathering processes.Here,we present a model to assess the roles played by incongruent carbonate dissolution and secondary calcite precipitation in modern weathering processes.We tested and applied the model to rivers draining the Himalayan–Tibetan region.The results suggest that regional aridity in the drainage basin promotes carbon sequestration as secondary carbonate but that for a given runoff,incongruent dissolution of carbonate possibly related to rapid physical erosion amplifies such sequestration.The isotopic compositions(^(13)C/^(12)C and^(18)O/^(16)O)of detrital carbonate transported by the main rivers in South and South-East Tibet imply that around 1%of the suspended material transported by those rivers corresponds to secondary carbonate and can represent between 5%and 15%of the alkalinity flux.Most of these alkalinity transported as particulate material is,nevertheless related to the weathering of carbonate lithologies and is also subjected to dissolution prior its final storage in sedimentary basins.However,on glacial-interglacial timescale this will amplify the significant role of mountain weathering on climatic variations.

Critical minimum temperature limits xylogenesis and maintains treelines on the southeastern Tibetan Plateau

Physiological and ecological mechanisms that define treelines are still debated. It has been suggested that the absence of trees above the treeline is caused by low temperatures that limit growth. Thus, we hypothesized that there is a critical minimum temperature （CTmin） preventing xylogenesis at treeline. We tested this hypothesis by examining weekly xylogenesis across three and four growing seasons in two natural Smith fir （Abies georgei var. srnithii） treeline sites on the southeastern Tibetan Plateau. Despite differences in the timing of cell differentiation among years, minimum air temperature was the dominant climatic variable associated with xylem growth; the critical minimum temperature （CTmin） for the onset and end of xylogenesis occurred at 0.7 ±0.4 ℃. A process-based modelling chronology of tree-ring formation using this CTmin was consistent with actual tree-ring data. This extremely low CTmin permits Smith fir growing at treeline to complete annual xylem production and maturation and provides both support and a mechanism for treeline formation.

Estimation of Critical Rainfall for Flood Disasters in the Qinghai-Tibet Plateau

According to the results of The Second Comprehensive Scientific Expedition on the Qinghai-Tibet Plateau,the balance of solid and liquid water on the Qinghai-Tibet Plateau is disturbed,and a large amount of solid water,such as glaciers and perpetual snow,is transformed into liquid water,which aggravates the risk of flood disasters in the Plateau.Based on the historical flood disaster records of the Qinghai-Tibet Plateau,this paper analyzed the temporal and spatial distribution characteristics of the flood disasters in the Plateau,and estimated the critical rainfall for the flood disasters combined with precipitation data from the meteorological stations in each basin of the Qinghai-Tibet Plateau.The results show that most of the flood disaster events in the Plateau are caused by precipitation,and the average annual occurrence of flood disasters is more than 30 cases and their frequency is on the rise.The high frequency areas of flood disasters in the Qinghai-Tibet Plateau are mainly in the Hehuang Valley and the Hengduan Mountains area;the secondary high frequency areas are located in the valley area of South Tibet and the peripheral area of the Hehuang valley.Finally,we found that the highest critical rainfall value of flood disasters in the Qinghai-Tibet Plateau is in the southern area of the plateau,followed by the eastern and southeastern parts of the plateau,and the lowest values are in the central,western and northern parts of the Plateau.